DISSERTATION RESEARCH: Origins of alternate ecosystem states - effects of drought on postfire tree regeneration and shifting dominance of western conifers

本博士论文研究旨在了解野火后的干旱如何影响落基山两种广泛分布的树种，洛奇波勒松和道格拉斯冷杉的建立。在黄石国家公园，变暖、干燥的环境导致严重野火的频率增加，这些野火会杀死现有的树木，并引发森林的再生。这些趋势预计将持续下去。黄石公园的许多树种都能很好地适应火灾。然而，火灾后早期和丰富的幼苗建立对森林恢复至关重要。树苗对干旱特别敏感，有证据表明，火灾后足够干燥的条件可能导致树苗大面积死亡，其后果可能持续数十年。这项研究将确定两种树种的幼苗如何对21世纪中期的干旱条件做出反应，并将确定影响幼苗对干旱条件反应的机制。这项研究的结果将促进对未来几十年美国西部森林如何应对环境变化的理解，并为正在努力应对野火增加的西部土地管理者提供有用的信息。除了提供重要的科学知识外，该研究还将为本科生提供体验森林生态领域研究的机会。研究人员还将吸引大黄石地区的当地居民，在当地商店举办科学艺术展，展示研究的照片。展览将附带一份讲义，向居民展示研究结果，例如森林变化如何影响娱乐机会。这项研究将解决以下问题：21世纪的干旱将如何改变广泛分布的西部针叶树的火灾后再生？未来的气候条件是否有利于非森林覆盖的替代优势树种？将进行一项温室试验，模拟预计生长季节日温度和土壤湿度条件的组合，以确定预期的干旱将如何影响不同土壤类型的火灾后树苗建立率。该实验将在威斯康星大学麦迪逊分校的一个独特设施中进行，该设施的环境条件可以控制在低于每日的分辨率，该工作将补充正在黄石进行的实地实验。结果将整合到基于过程的模型中，以探索干旱和增加的火灾活动在景观和区域尺度上的后果。

This doctoral dissertation research seeks to understand how drought following wildfires affects the establishment of two widespread Rocky Mountain tree species, lodgepole pine and Douglas-fir. In Yellowstone National Park, warming, drying conditions are leading to increased frequency of severe wildfires that kill existing trees and trigger regrowth of the forest. These trends are expected to continue. Many tree species in Yellowstone are well adapted to fire. Yet, early and abundant seedling establishment after fire is critical for forests to recover. Tree seedlings are particularly sensitive to drought, and evidence suggests that sufficiently dry postfire conditions could cause the widespread death of tree-seedlings, with consequences that may last decades. This research will determine how seedlings from two tree species respond to drought conditions expected in the mid-21st century and will identify the mechanisms that influence seedling response to dry conditions. The results of this study will advance understanding of how forests in the western United States will respond to environmental change over the coming decades and provide useful information for western land managers who are grappling with increased wildfires. In addition to providing important scientific knowledge, the study will provide opportunities for undergraduate students to experience research in the field of forest ecology. Researchers will also engage local residents of the Greater Yellowstone area by presenting an exhibit of science art in local shops that features photographs of the research. A handout will accompany the exhibit that presents the study findings to residents, such as how changing forests may influence recreational opportunities.This research will address the questions: How will 21st century drought alter postfire regeneration of a widespread western conifer? Will future climate conditions favor an alternate dominant tree species of non-forest cover? A greenhouse experiment will be conducted, where a combination of projected growing season daily temperature and soil-moisture conditions will be simulated to determine how expected drought will influence rates of postfire tree-seedling establishment in different soil types. The experiment will be conducted in a unique facility at the University of Wisconsin-Madison in which environmental conditions can be controlled at sub-daily resolutions, and the work will complement an ongoing field-based experiment in Yellowstone. Results will be integrated into process-based models to explore consequences of drought and increased fire activity at landscape and regional scales.